Fuel cell technology acquires ever more significance especially in connection with future drive concepts of vehicles. Fuel cells offer the possibility to convert chemically bonded energy directly into electrical energy which thereafter can be converted into mechanical drive energy with the aid of an electric motor. In contrast to thermal power engines, the efficiency of a fuel cell is not limited by a Carnot efficiency. Present day preferred fuel cells consume hydrogen and oxygen and convert these elements into the environmentally friendly end product “water”.
Because of the technical problems associated with hydrogen storage in vehicles, hydrogen as required is generated via a so-called reforming or partial oxidation of hydrocarbons. Hydrocarbons of this kind are present in the form of conventional fuels such as gasoline and diesel fuel; however, other hydrocarbons such as methane or methanol can also be used for this purpose. Special requirements are imposed on the corresponding arrangement for chemical conversion in connection with a fuel cell drive (that is, the reformation of fuel into water) compared to previous chemical systems.
One such arrangement must satisfy a considerable load range, that is, large differences in the necessary volume flow of hydrogen and, correspondingly, also the media necessary for generating the hydrogen. A corresponding dynamic performance for generating the desired fluctuations in the volume flow of the media within a short time must be ensured. In addition, an arrangement of this kind must offer an excellent cold start performance and a very substantial operational reliability. Further requirements with respect to the efficiency require a low weight in combination with a small volume and especially low manufacturing costs.
In fuel cell arrangements of the kind described, on the one hand, various media have to be supplied, that is, for example, water, fuel as well as air. On the other hand, one and the same medium, for example, fuel, must be supplied to different system components. Depending upon the configuration of the fuel cell arrangement, for example, a burner for generating the reaction heat for converting the fuel as well as the so-called reformer wherein the fuel is converted or a possible upstream vaporizer can all be supplied with the same fuel.
Likewise, as a rule, different components are to be supplied with water, for example, again the reformer for converting the fuel (for which a vaporizer can be connected upstream thereof, as required) as well as, for example, a unit, which is connected downstream of the reformer, for carrying out a so-called shift reaction in which residual quantities of CO, which result from the reaction in the reformer, are oxidized to CO2 under the addition of water whereby hydrogen is, in turn, released.
Up to now, a so-called metering pump is used for each fluid flow to be prepared in such fuel cell systems. The fluid flow of the particular medium needed in each case is supplied by the metering pump. Such metering pumps are very complex and correspondingly costly.